There has been known a bumper-stay mounting structure including: (a) a rear side member that is disposed along a longitudinal direction of a vehicle and that is deformed in its axial direction due to application of a load to its rear end portion at the time of rear end collision of the vehicle, thereby absorbing impact; (b) a bumper stay that is formed in a bottomed box shape, that has a bottom portion which is located in a rear portion of the bumper stay in the longitudinal direction of the vehicle and to which a bumper reinforcement is attached, and that is provided with, at an outer edge portion of an opening formed in a front portion of the bumper stay in the longitudinal direction of the vehicle that is opposite to the bottom portion, a pair of side flanges respectively extending outward to the left and the right from a pair of right and left side walls located on respective sides in a vehicle width direction and a lower flange extending downward from a lower side wall in a lower portion of the bumper stay in the height direction of the vehicle; and (c) a load transmission member that is disposed between the rear end portion of the rear side member and the bumper stay, that has a flat fastened portion that is fastened between the pair of side flanges and the lower flange of the bumper stay, and the rear end portion of the rear side member, and that transmits, to the rear side member via the fastened portion, a load input into the bumper stay from the bumper reinforcement at the time of the rear end collision of the vehicle.
A mounting structure as described in Patent Document 1 is one example thereof, and used in a case where there is performed the mounting of the bumper stay on a rear side member that has a bottom portion and a pair of side walls extending upward respectively from side portions of the bottom portion so as to form a substantially U-shaped cross section. In the mounting structure, (a) a rear end portion of the rear side member is provided with a pair of side flanges extending outward in a lateral direction of a vehicle respectively from the pair of side walls, and a lower flange extending downward from the bottom portion, and (b) the fastened portion of the load transmission member is configured to be fastened between the pair of side flanges and the lower flange of the bumper stay, and the pair of side flanges and the lower flange provided at the rear end portion of the rear side member. Further, as the load transmission member, an intermediate plate 100 provided with a pair of flanges 102, 104 to increase stiffness of a lower portion, as illustrated in FIG. 6, is employed, and the intermediate plate 100 is configured to be integrally fixed, together with the bumper stay, to the pair of side flanges and the lower flange of the rear side member with bolts or the like via three mounting holes 106. With this configuration, a load is transmitted to a lower side of the rear end portion of the rear side member, and it is expected that while the rear side member is deformed in a predetermined deformation form, a predetermined impact-absorption effect is obtained by the deformation.